Liquid crystal display devices have conventionally been used for desk calculators, electronic clocks, personal computers, etc. and in recent years there is an increasing demand therefor, and recently they are also applied to a wide range of applications such as mobile phones, tablet type terminals and the like. These liquid crystal display devices normally have a liquid crystal cell with a pair of polarizing plates disposed on the front and back sides of the liquid crystal cell to serve as a liquid crystal display panel.
In the recent market, as mobile devices such as mobile phones and tablet type terminals having a screen increased in size are widely used, there is a demand for reduction in weight and thickness of a constituent member thereof, namely a liquid crystal display panel, and there is a tendency to reduce a liquid crystal cell's glass, a front plate and/or the like in thickness. Furthermore, in order to eliminate reflection and scattering of light at an interface to enhance visibility, there is also a tendency to integrate the front plate with the liquid crystal display panel using a pressure sensitive adhesive, an ultraviolet curing type resin or the like.
Conventional liquid crystal display panels have a thick front plate and a thick liquid crystal cell, and their warping resulting from a polarizing plate's shrinkage has thus been suppressed even in high temperature environments. The above-mentioned recent tendency to reduce in thickness the front plate, the glass used for a liquid crystal cell and the like, however, results in warping of the liquid crystal display panel in use in high temperature environments, and it cannot be accommodated in a casing for a final product or other similar problems arise.
In order to suppress such warping of a liquid crystal display panel, a methodology has previously been developed to suppress the warping of the liquid crystal display panel by changing in thickness a polarizing plate to be disposed at the viewing side of a liquid crystal cell and a polarizing plate disposed on a side of the liquid crystal cell opposite to the viewing side (i.e., a back side thereof). For example, Japanese Patent Laying-Open No. 2012-058429 (PTD 1) describes a method for suppressing a liquid crystal display panel's warping by reducing the thickness of a polarizing film (a polarizer as referred to in the present invention) of a polarizing plate to be disposed at the viewing side of a liquid crystal cell to be smaller than the thickness of a polarizing film to be disposed at the back side of the liquid crystal cell.
However, a liquid crystal display panel's warping caused when the panel is used in a high temperature environment is attributed to a polarizing plate's shrinkage that depends upon a polarizer's thickness, as has been set forth above, and when the polarizer of the polarizing plate to be disposed at the viewing side is reduced in thickness, as described in PTD 1, a liquid crystal display panel having a front plate integrated using a pressure sensitive adhesive or an ultraviolet curing type resin or the like for improved visibility, in particular, may warp, and suppression of warping is thus not necessarily satisfactory.
Furthermore, Japanese Patent No. 4666430 (PTD 2) describes a liquid crystal display device which uses a plastic substrate liquid crystal cell (a liquid crystal display panel as referred to in the present invention) in which protective layers configuring polarizing plates disposed on the viewing side and back side of the liquid crystal cell are changed in thickness to suppress the plastic substrate liquid crystal cell's warping amount. This method does accomplish the purpose of suppressing warping of a liquid crystal cell. However, when the device is placed in a high temperature environment with the polarizing plate having the front plate integrated therewith for improved visibility, the method as described in PTD 2 wherein the protective layers are changed in thickness may cause the problems that the liquid crystal cell may be warped by the protective layer's thermal shrinkage and the device cannot be accommodated in a casing for a final product.